1. Field of the Invention
The present invention relates to a digital servo-control apparatus having feedforward function.
2. Description of the Prior Art
One type of servo-control apparatus that has analog feedforward function has heretofore been known.
In the analog feedforward control, the frequency of a command pulse is converted into a voltage, which is then added to the velocity command voltage and output to a servomotor driving circuit.
The conventional servo-control apparatus having the analog feedforward function suffers, however, from the problem that the feedforward value is delayed by a given time during the F/V conversion due to the time constant of hardware.
The above-described time lag (phase shift) causes a needless change of the command velocity. As a result, the servo system oscillates and chattering is generated on the machined surface of the workpiece, causing deformation of the finished configuration of the workpiece.